cant get colAUC to plot

Can someone please explain why this wont plot. The cats example given
for the colAUC function will plot.

Many thanks again
tom

#########################
library(caTools)
a<-rnorm(100)
b<-rbinom(100,1,0.7)
colAUC(a,b,plotROC=TRUE)

colAUC(a,b,plotROC=TRUE)

Error in strwidth(legend, units = "user", cex = cex) :
        argument "legend" is missing, with no default

R.Version()

$platform
[1] "x86_64-pc-linux-gnu"

$arch
[1] "x86_64"

$os
[1] "linux-gnu"

$system
[1] "x86_64, linux-gnu"

$status
[1] ""

$major
[1] "2"

$minor
[1] "1.0"

$year
[1] "2005"

$month
[1] "04"

$day
[1] "18"

$language
[1] "R"